Implantable sensor with wireless communication

ABSTRACT

An implantable sensor device, such as a pressure monitor, is implanted in the left ventricle (LV), in other heart chambers, or elsewhere, from which it wirelessly communicates pressure information to a remote communication device. The sensor device can be implanted using a placement catheter, an endoscope, or a laparoscope. The device can be secured entirely within the LV or heart wall, such as by using a corkscrew, a helical anchor, a harpoon, a threaded member, a hook, a barb, a fastener, a suture, or a mesh or coating for receiving fibrous tissue growth. The implantable sensor device provides less invasive chronic measurements of left ventricular blood pressure or other physical parameters. The wireless communication techniques include radio-telemetry, inductive coupling, passive transponders, and using the body as a conductor (referred to as “intracorporeal conductive communication” or a “personal area network”). Data from the receiver is downloadable into a computer for analysis or display.

FIELD OF THE INVENTION

This invention relates generally to an implantable sensor with wirelesscommunication, and particularly, but not by way of limitation, tophysiological monitoring of pressure or other parameters in humans andanimals using a monitor that is implantable within a heart chamber orelsewhere and is capable of wireless communication of sensor informationtherefrom.

BACKGROUND

The monitoring of fluid pressure within a body organ provides animportant tool for medical research and clinical diagnosis. For example,hydrocephalus and head injuries can cause body fluids to build up withinthe brain. The resulting fluid pressure buildup can result in death orserious brain damage. In another example, urinary dysfunction can causefluid pressure to build up in the bladder. In a further example,intrapleural pressure measurements can be used to monitor therespiration of infants who have been identified as being at risk forsudden infant death syndrome.

Blood pressure measurements are particularly important for medicalresearch and diagnosis for a variety of reasons. Such measurementsprovide researchers with insight into the physiology and functioning ofthe heart. Blood pressure measurements also provide researchers withuseful information regarding the safety and efficacy of pharmaceuticalsand the toxicity of chemicals. By transducing blood pressure into asignal waveform, a variety of useful parameters can be extracted. Theseparameters provide valuable information for the diagnosis of heartdisease. Left ventricular (LV) blood pressures measurements areparticularly important because the left ventricle chamber of the heartpumps blood to the systemic circulatory system, that is, throughout therest of the body.

Common parameters extracted from left ventricular blood pressurewaveforms include peak systolic pressure (the high pressure peakresulting from a contraction of the left ventricle chamber of theheart), end diastolic pressure (the low pressure valley resulting fromexpansion of the left ventricle), and maximum dP/dt (a peak value of howfast the pressure (P) changes with time (t) during a contraction of theleft ventricle). These blood pressure measurements provide helpfuldiagnostic information to the physician.

For example, maximum dP/dt provides a measure of the work that is beingdone by the heart. For certain conditions, such as congestive heartfailure (CHF), it is desired to reduce the work load on the heart. Thetreating physician can determine how effective a therapy is bydetermining if the treatment regimen has indeed reduced the work load onthe heart, as indicated by the maximum dP/dt signal extracted from theleft ventricular blood pressure waveform. Measurement of leftventricular blood pressure is also useful for titrating new drugs fortreating heart disease, that is, determining the desired dosage orconcentration of a new drug. Titrating new drugs requires information onhow these drugs are affecting the heart.

For example, beta adrenergic blocking drugs are often effective attreating arrhythmias and improving patient hemodynamics. However, suchdrugs are difficult to titrate. Because left ventricular blood pressureparameters, such as maximum dP/dt, provide information on how the heartis functioning, monitoring these parameters allows a physician to moreeasily determine the most appropriate dose of the drug for treating thepatient. The maximum dP/dt signal, if available, could also be used as afeedback mechanism in a system that automatically delivers therapy toadjust the work load of the heart. The delivery of therapy isautomatically adjusted based on the work load of the heart, as indicatedby the maximum dP/dt signal.

In another example, left ventricular blood pressure provides usefulinformation for controlling a cardiac rhythm management system. Cardiacrhythm management systems include, among other things, pacemakers, orpacers. Pacers deliver timed sequences of low energy electrical stimuli,called pace pulses, to the heart. Heart contractions are initiated inresponse to such pace pulses. By properly timing the delivery of pacepulses, the heart can be induced to contract in proper rhythm, greatlyimproving its efficiency as a pump. Pacers are often used to treatpatients with bradyarrhythmias, that is, hearts that beat too slowly, orirregularly. Cardiac rhythm management systems also includecardioverters or defibrillators that are capable of delivering higherenergy electrical stimuli to the heart. Defibrillators are often used totreat patients with tachyarrhythmias, that is, hearts that beat tooquickly. Such too-fast heart rhythms also cause diminished bloodcirculation because the heart isn't allowed sufficient time to fill withblood before contracting to expel the blood. Such pumping by the heartis inefficient. A defibrillator is capable of delivering an high energyelectrical stimulus that is sometimes referred to as a countershock. Thecountershock interrupts the tachyarrhythmia, allowing the heart toreestablish a normal rhythm for the efficient pumping of blood. Inaddition to pacers, cardiac rhythm management systems also include,among other things, pacer/defibrillators that combine the functions ofpacers and defibrillators, drug delivery devices, and any other systemsor devices for diagnosing or treating cardiac arrhythmias.

One example of using a cardiac rhythm management device to control heartrate in proportion to left ventricular blood pressure is described inMehra U.S. Pat. No. 5,129,394. The '394 patent, however, does notdisclose sensing actual left ventricular blood pressure. Instead, itdiscloses a pressure sensor located in the coronary vein. The coronaryvein extends from the right atrium through the heart tissue near theleft ventricle. Because of its small size, the coronary vein isdifficult to access for inserting a pressure sensor. Moreover, bloodpressure sensing in the coronary vein provides only an indirectapproximation of the actual left ventricular blood pressure.

Other existing techniques for monitoring left ventricular blood pressurealso have drawbacks. One technique of measuring left ventricular bloodpressure is described in Brockway et al. U.S. Pat. No. 4,846,191, whichis assigned to the assignee of the present application. The '191 patentdescribes a pressure sensor that is implanted in the abdomen of alaboratory animal. The pressure sensor is connected to an organ, such asthe heart or the brain, via a fluid-filled pressure transmittingcatheter (PTC). One limitation of this device is that it requiresinvasive access to the organ in which fluid pressure is to be monitored.

For example, in monitoring left ventricular pressure, one surgicaltechnique for using the device described in the '191 patent involvesperforming a highly invasive laparotomy procedure. In this procedure,the pressure transmitting catheter is passed through an incision in thediaphragm and an incision into the apex (bottom tip) of the heart. Thehigh blood pressure in the left ventricle further increases the risk ofmaking such incisions directly into the left ventricle. This proceduretypically requires a two week recovery period for the laboratory animal.Moreover, because catheterization of the apex involves significantrisks, this technique would likely be considered too invasive for humanuse.

Alternatively, an incision may be made into the aorta, which is theprimary artery carrying blood from the left ventricle to the rest of thebody. The pressure transmitting catheter is then passed into the aorticincision for measuring blood pressure in the aorta. Aortic incisions arealso problematic because of the high blood pressure in the arterialcirculatory system. Moreover, measuring blood pressure in the aorta doesnot provide a direct measurement of blood pressure in the leftventricle; such information is unavailable, for example, when the aorticvalve is closed. Alternatively, the pressure transmitting catheter couldbe passed through the aortic valve into the left ventricle. However,leaving the pressure transmitting catheter extending through the aorticvalve for a long period of time risks damage to the aortic valve as aresult of the high blood pressure in the left ventricle. Thus, thisprocedure is also likely unsuitable for human use, particularly forchronic left ventricular blood pressure monitoring, i.e., monitoringover an extended period of time.

Another technique for measuring left ventricular blood pressure isdescribed in Pohndorf et al. U.S. Pat. No. 5,353,800. A distal end of apressure sensing lead is transvenously introduced into the rightventricle of the patient's heart. A hollow needle at the distal end ofthe lead is punched through the ventricular septum, that is, through thewall separating the right and left ventricles. This provides access tothe left ventricle for sensing pressure gradients that are communicatedthrough the hollow needle to a pressure sensor that is outside of theleft ventricle. Because this procedure involves invasively forming anopening in the septum, it creates significant risks for human cardiacpatients who are likely already very sick and vulnerable to such risks.

A further technique for measuring left ventricular blood pressure uses apressure sensing catheter, such as a “Millar catheter,” available fromMillar Instruments, Inc., of Houston, Tex. The pressure sensing catheteris passed through the left atrium and through the mitral valve (whichseparates the left atrium and left ventricle) into the left ventricle.As discussed above, however, high blood pressures exist in the leftventricle, which would likely result in damage to the mitral valve ifthe catheter were left interposed in the mitral valve for a long periodof time. As a result, if a sequence of successive measurements is to beobtained over a long period of time, the patient must undergorecatheterization for each measurement. However, catheterization itselfinvolves risk, discomfort, and expense, making multiple catheterizationsof the patient very undesirable.

In summary, present techniques for measuring left ventricular pressureare too invasive for human use and unsuitable for use over an extendedperiod of time. Physicians and researchers need less invasive techniquesfor chronic measurement of left ventricular blood pressure, both fordiagnosing heart conditions and for determining whether therapydelivered to the heart is adequate for effectively treating thepatient's symptoms.

SUMMARY

The present system provides, among other things, a less invasiveimplantable sensor device capable of wirelessly communicating sensorinformation. The sensor is implantable in a heart chamber, in other bodyorgans and body cavities, and elsewhere within a living organism. Oneexample includes a blood pressure monitoring device that is suitable foruse over an extended period of time in the left ventricle for wirelesslycommunicating blood pressure information therefrom. This provides lessinvasive chronic pressure measurements in the left ventricle. As aresult, the risk of obtaining such important measurements is reduced.This enables a physician to more accurately diagnose and treat seriousheart conditions. It also enables a biomedical researcher to monitorsensor signals in animal research studies.

In one example, the wirelessly communicated left ventricular bloodpressure information is used to control the delivery of therapy by acardiac rhythm management device. In another example, the present systemadvantageously allows a physician to obtain a sequence of leftventricular blood pressure measurements over a long period of time. Bycontrast, using a pressure sensing catheter for obtaining suchmeasurements over a long period of time risks damaging heart valvesbecause of the high blood pressures that exist in the left ventricle.Because the present system allows long term monitoring, it can be used,for example, in assessing circadian variations in physiological dataover a period of time. Such information is potentially valuable indiagnosing and treating patients. See, e.g., Brian P. Brockway, Perry A.Mills, and Sylvia H. Azar, “A New Method For Continuous ChronicMeasurement and Recording of Blood Pressure, Heart Rate, and Activity inthe Rat via Radio-Telemetry,” Clinical and ExperimentalHypertension—Theory and Practice, A13(5), pp. 885-895 (1991), which isincorporated herein by reference in its entirety.

Certain particular embodiments of the invention are summarized below, byway of illustrative example, but not by way of limitation. The scope ofthe invention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

One aspect of the invention provides an apparatus for sensing aparameter in a heart chamber in a heart in a living organism. Theapparatus includes a sensor and a wireless communication circuit. Thesensor is adapted for being disposed in the heart chamber. The sensorprovides a sensor signal based on the parameter sensed in the heartchamber. The wireless communication circuit is adapted for beingdisposed in the heart chamber. The communication circuit is coupled tothe sensor and transmits information out of the heart chamber based onthe sensor signal. The wireless communication techniques includeradio-telemetry, reactive coupling, passive transponders, andintracorporeal conductive communication.

In one embodiment, the sensing apparatus includes a housing carrying thesensor and the communication circuit and at least one stabilizer that iscoupled to the housing. Also included in the housing is a battery which,in one embodiment, is recharged by energy received from outside theheart chamber. A receiver, external to the heart chamber, iscommunicatively coupled to the communication circuit for receiving theinformation based on the sensor signal. In one embodiment, the receiveris carried by a cardiac rhythm management system, and therapy deliveredby the cardiac rhythm management system is adjusted according toinformation wirelessly received from the sensor device implanted in theheart chamber. In another embodiment, the receiver is coupled to acomputer that analyzes or displays the information from the sensor. Inone embodiment, the sensor is a pressure transducer, however, othersensors may also be used.

Another aspect of the invention includes a method of sensing a parameter(e.g., blood pressure) in a heart chamber in a heart in a livingorganism. A physical manifestation of the parameter in the heart chamberis received at a sensor disposed within the heart chamber, where it istransduced into a sensor signal. Information based on the sensor signalis wirelessly communicated from the heart chamber. A further embodimentincludes translumenally disposing the sensor in the heart chamber.

One embodiment of communicating the information includes using a passivetransponder. In this technique, energy is received from outside theheart at a passive transponder that is in the heart. The passivetransponder is powered from the energy received from outside the heartchamber. Information is transmitted from the heart chamber using thepowered passive transponder. In another embodiment, energy received fromoutside the heart chamber is used to recharge a battery that is locatedin the heart chamber.

Another embodiment of communicating information includes usingintracorporeal conductive communication, which uses the living organismas the conductor. In this technique, a current is conducted through atleast a portion of the living organism. A signal that is based on thiscurrent is received at a receiver that is outside the heart chamber. Inone embodiment, the receiver is carried by an implantable medical devicelocated within the living organism such as, for example, a cardiacrhythm management device. Therapy delivered by the cardiac rhythmmanagement device is adjusted based on the signal received byintracorporeal conductive communication or other wireless communicationtechnique. In another embodiment, the receiver is external to the livingorganism, and information is stored in a memory in the receiver.

Another aspect of the invention provides a method. The method includesinducing a current between first electrodes implanted in a livingorganism. The current at the first electrodes is modulated with a datasignal. A signal based on the current is demodulated at secondelectrodes. In one embodiment, the second electrodes are also implantedin the living organism.

Another aspect of the invention provides a catheter. The catheterincludes an elongate member having first and second ends. The first endof the elongate member includes a cavity adapted for carrying animplantable measurement device that includes a wireless communicationcircuit. The elongate member also includes a lumen extendingsubstantially between the cavity and the second end of the elongatemember. An engaging member is carried by the cavity. The engaging memberis extendable outwardly from the cavity at the first end of the elongatemember. The engaging member is operatively coupled to a manipulator atthe second end of the elongate member. The engaging member is adaptedfor engaging the implantable measurement device. In one embodiment,portions of the elongate member are flexible such that the catheter isadapted for translumenal access to a heart chamber. Other aspects of theinvention will be apparent on reading the following detailed descriptionof the invention and viewing the drawings that form a part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like numerals describe substantially similar componentsthroughout the several views.

FIG. 1 is a schematic diagram illustrating generally one embodiment ofportions of a sensor system, such as a pressure monitor system, and anenvironment in which it is used.

FIG. 2 is a schematic diagram illustrating generally an embodiment ofcertain external portions of the system.

FIG. 3A is a schematic/block diagram illustrating generally oneembodiment of a portion of an implantable sensor device, such as animplantable pressure monitor device including a corkscrew stabilizer.

FIG. 3B is a schematic/block diagram illustrating generally oneembodiment of an implantable sensor device, such as an implantablepressure monitor device including a harpoon or barbed stabilizer.

FIG. 3C is a schematic/block diagram illustrating generally oneembodiment of an implantable sensor device, such as an implantablepressure monitor device including a mesh stabilizer and a corkscrewstabilizer.

FIG. 3D is a schematic/block diagram illustrating generally oneembodiment of an implantable sensor device, such as an implantablepressure monitor device including a deformable stabilizer.

FIG. 4 is a schematic diagram illustrating generally one embodiment ofthe present system using wireless communication, such as intracorporealconductive communication, between an implanted medical device, such ascardiac rhythm management system, and an external remote receiver.

FIG. 5 is a schematic diagram illustrating generally one embodiment ofthe present system using wireless communication, such as intracorporealconductive communication, between an implanted sensor device and animplanted remote receiver that is carried by an implanted medical devicesuch as by cardiac rhythm management system.

FIG. 6 is a cross-sectional schematic diagram illustrating generally oneembodiment of a placement catheter for implanting a sensor device, suchas an implantable pressure monitor device.

FIG. 7 is a schematic diagram illustrating another embodiment of animplantable sensor device, such as a pressure monitor, having a housingthat is substantially implanted within tissue, such as the interior wallof a heart chamber.

FIG. 8 is a schematic diagram illustrating generally another embodimentof a sensor device for implantation substantially within tissue andhaving a substantially flexible anchor.

FIG. 9 is a schematic diagram illustrating generally another embodimentof a sensor device for implantation substantially within tissue andhaving a substantially rigid anchor.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims and their equivalents. In thedrawings, like numerals describe substantially similar componentsthroughout the several views.

This document describes, among other things, an implantable sensor, suchas a pressure monitor. The sensor device is implanted in a heart chamber(or elsewhere) and wirelessly communicates information therefrom. In oneembodiment, the sensor device is capable of providing less invasivechronic measurements of pressure, such as, by way of example, but not byway of limitation, measurements of blood pressure in the left ventricleof the heart. The implantable pressure monitor reduces the risk ofobtaining such important measurements, enabling a physician to moreaccurately diagnose and treat serious heart conditions.

System Overview

FIG. 1 is a schematic diagram illustrating generally, by way of example,but not by way of limitation, one embodiment of portions of a sensorsystem, such as pressure monitor system 100, and one environment inwhich system 100 is used. In FIG. 1, system 100 includes a sensordevice, such as an implantable pressure monitor device 105. Device 105is introduced into a living. organism, such as in a heart chamber orother organ or body cavity. Miniature implantable device 105 is capableof measuring internal body pressure, such as in humans or animals.Aspects of one embodiment of device 105 and its operation are describedin Brockway et al. U.S. Pat. No. 4,846,191 entitled “Device For ChronicMeasurement of Internal Body Pressure,” which is assigned to theassignee of the present application, and which is incorporated herein byreference in its entirety.

In FIG. 1, device 105 is implanted in a heart 110 of a human patient115. Heart 110 includes several heart chambers, such as a right atrium120, a right ventricle 125, a left atrium 130, and a left ventricle 135.In this particular example, device 105 is implanted, using a placementcatheter, inside left ventricle 135 where it is stabilized, such as bysecuring the device 105 to an interior wall of left ventricle 135.However, in other embodiments, device 105 is implanted in one of theright atrium 120, right ventricle 125, left atrium 130, or within otherorgans or body cavities. Device 105 can be introduced into the bodytranslumenally (e.g., transvenously or transarterially), endoscopically,laparoscopically, or otherwise (e.g., during open heart surgery).

In this embodiment, system 100 also includes an implantable or externalreceiver 140 or other receiver, transceiver, transponder, orcommunication device. Device 105 wirelessly communicates pressureinformation from the organ in which device 105 is located, such as byusing radio telemetry or any other wireless communication technique. InFIG. 1, left ventricular blood pressure information is communicated bydevice 105 and received by an external receiver 140 worn by the patient.In one embodiment, receiver 140 includes a memory or recording devicefor storing the pressure information received from device 105. In afurther embodiment, receiver 140 includes a real time clock fortime-stamping the pressure information with the time at which theinformation is received at receiver 140.

FIG. 2 is a schematic diagram illustrating generally, by way of example,but not by way of limitation, another embodiment of portions of system100. In FIG. 2, pressure information that was stored in the memory orrecording device of receiver 140 is transferred into computer 200, suchas via an electrical coupling cable 205, or alternatively via opticalcommunication, or using any other wired or wireless communicationtechnique. In one embodiment, computer 200 includes a processor forperforming statistical or other signal processing or analysis of thepressure information. In another embodiment, computer 200 includes adisplay 202 for allowing the physician or other care giver to review andanalyze the pressure data. In one example, display 202 includesdiagnostic indicators based on analysis of the pressure data by computer200. In a further embodiment, computer 200 includes a memory forarchival of raw or processed pressure information. For example, thepressure information can be electronically appended to the patient'smedical record in a computer database.

Implantable Pressure Monitor

FIG. 3A is a schematic/block diagram illustrating generally, by way ofexample, but not by way of limitation, one embodiment of device 105. Inthis embodiment, device 105 includes a housing 300 carrying a sensor,such as pressure transducer 305, and a communication circuit 310.Housing 300 is adapted for implantation in a living organism such as ahuman or animal. In one example, housing 300 is implanted within a bodycavity or an organ, such as within a heart chamber (e.g., left ventricle135) of heart 110.

In one embodiment, device 105 includes a stabilizer 312A extendingoutward from housing 300 to stabilize or secure device 105 at aparticular location in the heart chamber or other organ in which device105 is implanted. FIG. 3A illustrates a corkscrew stabilizer 312A which,in one embodiment, includes a solid coiled needle extendinglongitudinally outward from housing 300. By rotating device 105,corkscrew stabilizer 312A is screwed into the wall of the heart chamberor other organ in which device 105 is disposed, thereby securing device105 at a particular location in the body. The corkscrew stabilizer 312Ais used with or without one or more barbs. The barbs are located, forexample, at a tip distal from device 105, or at different locationsalong the helical length of stabilizer 312A. In one embodiment, thesurface of corkscrew stabilizer 312A is coated or otherwise prepared topromote the growth of fibrotic tissue to reliably secure device 105 tothe heart wall or other desired location.

FIG. 3B illustrates generally one embodiment of a harpoon stabilizer312B, providing an approximately straight outward extension from housing300, and including a barb or hook at its distal tip. FIG. 3C illustratesgenerally one embodiment of a mesh stabilizer 312C, extending outwardfrom or integrally formed with housing 300. Mesh stabilizer 312C alsopromotes the ingrowth of adjacent fibrous tissue to assist in securingdevice 105 at a particular location. FIG. 3D illustrates generally oneembodiment of a flexible or expanding deformable stabilizer 312D. In oneembodiment, stabilizer 312D is made of a flexible, spring-like, ordeformable material or a “memory metal.” As illustrated in FIG. 3D,stabilizer 312D maintains a compact shape during implantation, butdeforms or expands in profile after device 105 is implanted into theheart chamber or other body cavity. As a result of this deformation orexpansion, stabilizer 312D tends to hold device 105 within the bodycavity in which it is implanted. The above-discussed stabilizers 312 canalso be used in combination with each other, such as illustrated in FIG.3C.

FIGS. 3A-3D illustrate particular embodiments of device 105 in which theinternal pressure of the organ is provided to pressure transducer 305via a pressure communication apparatus such as, by way of example, butnot by way of limitation, a flexible or rigid pressure transmittingcatheter (PTC) 315. In one embodiment, pressure transmitting catheter315 senses a pressure at one or more pressure-sensitive mechanisms(e.g., a diaphragm, gel-like cap, or other compliant structure) at itsdistal tip 320. Pressure transmitting catheter 315 communicates thepressure, via a bore, shaft, or lumen 325, to its proximal end 330 thatinterfaces with transducer 305. Lumen 325 extends substantially betweendistal tip 320 and proximal end 330 of pressure transmitting catheter315. In one embodiment, lumen 325 is filled with a pressure-transmittingmedium, such as a fluid of any viscosity, a gel-like material, acombination of fluid and gel-like material, or any other flowablemedium. In one embodiment, by way of example, but not by way oflimitation, distal tip 320 includes a biocompatible andpressure-transmitting gel cap for transmitting substantiallysteady-state and/or very low frequency pressure variations, and distaltip 320 also includes a thin-wall compliant structure for transmittingpressure variations at higher frequencies. Lumen 325 is filled with apressure-transmitting fluid retained within lumen 325 by the gel cap.The gel cap also prevents body fluids from entering lumen 325.Similarly, in one embodiment, proximal end 330 includes one or morepressure-transmitting mechanisms (e.g., a diaphragm, gel-like cap, orother compliant structure), which also retains the pressure-transmittingfluid in lumen 325. Although one embodiment of device 105 includespressure transmitting catheter 315, the technique of communicatingpressure to pressure transducer 305 is not limited to using pressuretransmitting catheter 315. For example, device 105 alternativelyprovides a pressure transmitting mechanism that is integrally formedwith housing 300 of device 105 rather than extending outwardlytherefrom. Other embodiments of device 105 include the use of any othertechnique of receiving pressure at pressure transducer 305.

Pressure transducer 305 receives the pressure communicated by pressuretransmitting catheter 315, or by any other pressure communicationmechanism, at the interface at its proximal end 330. In response,pressure transducer 305 provides an electrical pressure signal thatincludes pressure information, such as steady-state pressure orvariations in pressure. In one embodiment, pressure transducer 305includes a semiconductor resistive strain gauge, the resistance of whichvaries according to the pressure communicated by pressure transmittingcatheter 315. Transducer 305 is electrically coupled to communicationcircuit 310 and provides the electrical pressure signal to communicationcircuit 310.

Communication Techniques

Communication circuit 310 wirelessly transmits pressure information fromdevice 105 to remote receiver 140 (or other receiver, transceiver,transponder, or communication device) by radio telemetry or any otherwireless data communication technique. In one embodiment, communicationcircuit 310 includes or is coupled to an antenna for wirelesscommunication. However, the antenna need not be located withincommunication circuit 310. In another embodiment, communication circuit310 also includes signal processing circuits, such as amplification andfiltering circuits that process the electrical pressure signal receivedfrom pressure transducer 305, or analog-to-digital conversion circuits,or a microprocessor or other circuit for performing data analysis ordata compression. In a further embodiment, communication circuit 310also includes a memory device for storing the pressure information,other data, or operating parameters of device 105. In yet anotherembodiment, communication circuit 310 includes a real-time clock fortime-stamping the pressure information.

In one embodiment, at least one of communication circuit 310 ortransducer 305 is powered by an internal power source such as a lithiumor other suitable battery 335. In another embodiment, communicationcircuit 310 is a passive transponder that is not powered by an internalpower source. Instead, communication circuit 310 receives energywirelessly from a remote source, such as an energy source external tothe body of the patient in which device 105 is implanted. Communicationcircuit 310 is powered by the energy that it receives wirelessly fromthe external source. In another embodiment, battery 335 is rechargeableand device 105 includes an energy reception circuit that is coupled tobattery 335. The energy reception circuit in device 105 wirelesslyreceives energy from a remote source, such as an energy source that isexternal to the body of the patient in which device 105 is implanted.The energy that is received by the energy reception circuit in device105 is used by the energy reception circuit to recharge battery 335.

In one example of passive transponder technology, communication circuit310 includes a first inductance, such as a coil. A second inductance,such as a coil, is placed outside the body, for example, at a locationthat is close to the site of the implanted device. The first and secondinductances are inductively coupled for wireless energy transmissionfrom the external second inductance to the implanted first inductance,and for wireless data communication from the implanted first inductanceto the external second inductance. System 100 may incorporate otherpassive transponder techniques as well.

In one embodiment, communication circuit 310 wirelessly communicatespressure information from device 105 to external remote receiver 140using an intracorporeal conductive communication device (also referredto as “near-field intrabody communication” or a “personal areanetwork”). In this document, wireless communication refers to anycommunication technique that does not use a wire or optical fiber.Wireless communication includes either or both of unidirectional and/orbidirectional communication. The unidirectional or bidirectionalcommunication is carried out between any combination of implanted and/orexternal communication devices. In various embodiments, certain ones ofthe communication devices are carried by implanted sensor devices (suchas an implanted pressure monitor), implanted medical devices (such as animplanted cardiac rhythm management device), and external communicationdevices for communication therebetween. Wireless communication includes,but is not limited to: radio telemetry, reactive coupling, andintracorporeal conductive communication. In this document,intracorporeal conductive communication refers to any communicationtechnique that uses a living organism (e.g., the body of a human oranimal) as a conductor for communicating data. In one embodiment,wireless communication is used to program operating parameters inimplanted device 105.

In one example of an intracorporeal conductive communication device,communication circuit 310 is electrically coupled to electrodes locatedon housing 300 and insulated from each other. Communication circuit 310capacitively couples a very low (e.g., less than a stimulation thresholdof heart 110) displacement current that is conducted through the body toremote receiver 140. The current is modulated with a data signal. Thedata signal includes the pressure information or other data to bewirelessly communicated from the implanted medical device 105. In thisembodiment, the resulting current is detected at remote receiver 140 byelectrodes that contact the body of patient 115 during the wirelesscommunication from device 105. The detected current is demodulated toobtain the pressure information or other data. The use of intracorporealconductive communication techniques is described in Coppersmith et al.U.S. Pat. No. 5,796,827 entitled “System and Method for Near-FieldHuman-Body Coupling For Encrypted Communication With IdentificationCards,” and in T. G. Zimmerman, “Personal Area Networks: Near-fieldintrabody communication,” IBM Systems Journal, Vol. 35, No. 3 & 4, 1996,each of which is incorporated herein by reference in its entirety.

In one embodiment, system 100 includes, among other things,communicating information from any implanted medical device to anexternal remote receiver 140 using intracorporeal conductivecommunication (i.e., using the body as a conductor). Examples of suchimplanted medical devices include, but are not limited to: pressuremonitors, cardiac pacemakers, defibrillators, drug-delivery devices, andcardiac rhythm management devices.

FIG. 4 is a schematic diagram illustrating generally, by way of example,but not by way of limitation, one embodiment of system 100 using eitherunidirectional or bidirectional intracorporeal conductive communicationbetween an implanted medical device, such as cardiac rhythm managementdevice 400, and an external remote receiver 140. This includes, forexample, intracorporeal conductive communication of data from electrodes405A-B at the cardiac rhythm management device 400 to electrodes 410A-Bat the external remote receiver 140, as well as programming operatingparameters of cardiac rhythm management device 400 based on instructionsreceived via intracorporeal conductive communication from externalremote receiver 140.

FIG. 5 is a schematic diagram illustrating generally, by way of example,but not by way of limitation, another embodiment of system 100 usingeither unidirectional or bidirectional intracorporeal conductivecommunication between electrodes 505A-B at pressure monitor device 105,which is implanted in left ventricle 135, and electrodes 405A-B coupledto an implanted remote receiver 140 carried by an implanted medicaldevice, such as by cardiac rhythm management device 400. In oneembodiment, cardiac rhythm management device 400 includes a therapygenerator that is coupled to heart 110 through a leadwire. In thisembodiment, device 105 senses left ventricular blood pressure andcommunicates, via intracorporeal conductive communication, leftventricular blood pressure information to cardiac rhythm managementdevice 400 where it is received by implanted receiver 140. Based on thereceived pressure information, cardiac rhythm management device 400adjusts therapy delivered to heart 110. In one example, cardiac rhythmmanagement device 400 is a pacer or pacer/defibrillator that adjusts therate of delivering electrical pacing pulses to heart 110 via leadwire500 based on the left ventricular pressure information received fromdevice 105. In another example, cardiac rhythm management device 400 isa defibrillator or pacer/defibrillator that delivers antitachyarrhythmiatherapy to heart 110 based on the left ventricular pressure informationreceived from device 105. Similarly, system 100 includes usingintracorporeal conductive communication to transmit information todevice 105 from another implanted medical device, such as cardiac rhythmmanagement device 400. Moreover, the embodiments described with respectto FIGS. 4 and 5 can be combined for communication between any of one ormore implanted medical devices, one or more implanted sensor devicessuch as device 105, and/or one or more external or implanted remotereceivers 140.

Implantation and Use

FIG. 6 is a cross-sectional schematic diagram illustrating generally, byway of example, but not by way of limitation, one embodiment of aplacement catheter 600 for implantably disposing device 105 in a heartchamber, such as left ventricle 135. Catheter 600 includes an at leastpartially flexible elongate member having a proximal end 600A that ismanipulated by the user. Catheter 600 also includes a distal end 600B ofthe elongate member that is inserted in the patient 115. In oneembodiment, the distal end 600B of catheter 600 includes a cavity 605carrying at least a portion of device 105. Cavity 605 iscircumferentially encompassed by a sheath 607 that, in one embodiment,is open at distal end 600B of catheter 600.

Catheter 600 also includes at least one engaging member, such as plunger610. Plunger 610 engages device 105. In one example, an inner surface ofplunger 610 includes protrusions, such as pins 615, that engagereceptacles 620 or other indentations in housing 300 of device 105.Plunger 610 is controlled at proximal end 600A of catheter 600 by amanipulator, such as handle 625. Handle 625 is coupled to plunger 610 bya coupling member 630, such as one or more rods or cables extendinglongitudinally within catheter 600. Plunger 610 is capable oflongitudinal motion toward and away from distal end 600B of catheter600, so that device 105 can be advanced from or retracted toward cavity605. Plunger 610 is also capable of rotational motion, by manipulatinghandle 625, so that corkscrew stabilizer 312A can be rotatably screwedinto tissue such as the heart wall. Pins 615 engage receptacles 620 toensure that device 105 rotates together with plunger 610.

In one embodiment, catheter 600 also includes a safety tether 635, whichis looped through an opening or other feature in housing 300 of device105. Tether 635 extends longitudinally through catheter 600 towardproximal end 600A, where the looped tether 635 is knotted or otherwisesecured at a tether keep 640 on handle 625 or elsewhere. Tether 635secures device 105 to catheter 600 until final release of device 105 isdesired, at which time tether 635 is cut.

In another embodiment, catheter 600 includes a convex cap 640 at distalend 600B. Convex cap 640 eases the translumenal travel of catheter 600through a blood vessel or other constriction. In one example, cap 640 ishinged to catheter 600, such as at sheath 607, so that cap 640 opensoutwardly from distal end 600B when device 105 is pushed out of cavity605. In another example, cap 640 includes one or more deformable flapsthat similarly open outwardly to allow device 105 to be advanced outfrom cavity 605 by pushing device 105 against cap 640. In a furtherembodiment, cap 640 includes a material that is soluble in body fluidsafter a predetermined time period. In this embodiment, cap 640 dissolvesafter catheter 600 is translumenally guided to left ventricle 135 orother desired location. After cap 640 dissolves, device 105 is advancedlongitudinally outward from cavity 605 at distal end 600B of catheter600. In another embodiment of the invention, cap 640 is omitted suchthat cavity 605 is open to distal end 600B of catheter 600 even duringtranslumenal insertion.

In one example, catheter 600 is used to place device 105 in a heartchamber, such as left ventricle 135. One such technique includesinserting catheter 600 into the patient 115, such as via the subclavianartery. Catheter 600 is translumenally guided through the artery,through the left atrium, and through the mitral valve until its distalend 600B is within left ventricle 135. Progress of the catheter 600, asit travels from the insertion point to the left ventricle 135, istypically monitored on a display using fluoroscopy. This assists thephysician in translumenally steering catheter 600 along the proper pathto a desired location in left ventricle 135. In the embodiment of device105 illustrated in FIG. 3A, which includes a corkscrew stabilizer 312A,sheath 607 and/or cap 640 prevents the sharp tip of corkscrew stabilizer312A from damaging the blood vessel while device 105 is beingtranslumenally maneuvered through the blood vessel.

In one embodiment, placement catheter 600 has high torsional stabilityand is steerable. In this embodiment, sheath 607 and portions ofcatheter 600 near its distal end 600B are substantially rigid. Catheter600 is adapted for receiving, at its proximal end 600A, a removablestylet that extends longitudinally along catheter 600. The styletextends approximately to (or slightly beyond) a distal end of couplingmember 630. A straight stylet is typically employed until distal end600B of catheter 600 enters heart 110. Then, the straight stylet isremoved from catheter 600 and a stylet having a curved or bent distalend is inserted in its place. By rotating the bent stylet as catheter600 is advanced into heart 110, the distal end 600B of catheter 600 isdirected to the desired location in left ventricle 135 or other heartchamber.

When device 105 is positioned at a desired location in left ventricle135, plunger 610 is advanced slightly so that corkscrew stabilizer 312Aprotrudes outwardly from cavity 605 and contacts the heart wall in theinterior of left ventricle 135. Handle 625 is rotated which, in turn,rotates plunger 610 together with device 105, such that corkscrewstabilizer 312A is screwed into the heart wall to secure device 105 inposition (e.g., at the apex of left ventricle 135 or other desiredlocation). After securing device 105, plunger 610 is advanced further.Plunger 610 is designed to open outwardly when it is extended outside ofsheath 607. As a result, pins 615 disengage from receptacles 620,releasing the grip of plunger 610 on device 105. Tether 635 is then cut(at proximal end 600A of catheter 600) and removed, thereby releasingdevice 105. Catheter 600 is then withdrawn from the subclavian artery.

FIG. 7 is a schematic diagram illustrating generally, by way of example,but not by way of limitation, another embodiment of device 105 and anenvironment in which it is used. In FIG. 7, housing 300 of device 105 issubstantially implanted within the myocardium at the interior wall ofleft ventricle 135 of heart 110. The pressure transmitting catheter 315portion of device 105 extends outwardly from housing 300 into leftventricle 135 for sensing blood pressure its distal tip 320. In thisembodiment, deformable stabilizer 312D is integrated with a sharpenedend of housing 300 so that housing 300 can be advanced into the heartwall. Then, the deformable stabilizer 312D is expanded in a spring-likefashion to secure device 105 at the desired location. Device 105 isimplanted using a placement catheter 600 as described with respect toFIG. 6. In one embodiment, housing 300 is designed to promote fibrousingrowth, such as by properly preparing housing 300 with a coatingand/or surface roughening, or by incorporating a mesh or fabric into theouter surface of housing 300.

FIG. 8 is a schematic diagram illustrating generally, by way of example,but not by way of limitation, another embodiment of device 105 that iscapable of being implanted substantially within the interior wall ofleft ventricle 135 of heart 110. In this embodiment, device 105 includesa helical anchor 800 surrounding a portion of device 105. In oneembodiment, anchor 800 includes a highly elastic metal such as, forexample, a memory metal such as nitinol. A spring constant of anchor 800is low enough to allow anchor 800 to conform to housing 300 of device105 while torsional force is being applied to insert device 105 into themyocardial tissue 805 or other tissue. Upon release of this torsionalforce, anchor 800 deforms, such as, for example, by returning to itsoriginal shape. This results in the application of force to thesurrounding myocardial tissue 805 for securing a portion of device 105to the tissue. In one embodiment, more than one anchor 800 is includedsuch as, for example, an anchor 800 at both proximal end 300A and distalend 300B of housing 300 of device 105. In another embodiment, housing300 of device 105 includes a head 810 portion at proximal end 300A. Head810 limits the advance of device 105 within myocardial tissue 805. Thisensures that device 105 has access to the left ventricle 135 or otherheart chamber to allow accurate blood pressure measurements in the heartchamber. This also reduces the risk of fibrous tissue growing over thepressure-sensitive portion of device 105, such as pressure transmittingcatheter 315.

FIG. 9 is a schematic diagram illustrating generally, by way of example,but not by way of limitation, another embodiment of device 105 that iscapable of being implanted substantially within myocardial tissue 805.In this embodiment, device 105 includes a substantially rigid helicalmetal coil (e.g., a titanium coil) anchor 800 surrounding a portion ofhousing 300 of device 105. Anchor 800 has a profile similar to that ofdevice 105, as illustrated in FIG. 9. Upon application of a torsionalforce, anchor 800 screws into the heart wall. In another embodiment,more than one anchor 800 is included such as, for example, an anchor 800at both proximal end 800A and distal end 800B.

Conclusion

The present system includes, among other things, a sensor device such asa pressure monitor. The sensor device is implantable in a heart chamberor elsewhere, and it wirelessly communicates sensor informationtherefrom. In one embodiment, an implantable pressure monitor providesless invasive chronic measurements of pressure, such as, by way ofexample, but not by way of limitation, measurements of left ventricularblood pressure. The implantable pressure monitor reduces the risk ofobtaining such important measurements, enabling a physician to moreaccurately diagnose and treat serious heart conditions.

Though particular aspects of the system have been described inconjunction with its use in measuring left ventricular blood pressure,it is understood that the system can also be used for measuring pressureelsewhere. For example, but not by way of limitation, the system canalso be used for measuring pressure in other heart chambers, bloodvessels (e.g., pulmonary artery), body organs (e.g., the bladder,kidney, uterus), or body cavities (e.g., for intracranial, intraocular,or intrapleural pressure measurements). Moreover, though translumenalimplantation has been described using a placement catheter, the presentsystem also includes implantation using an endoscope, laparoscope, orother minimally invasive or other surgical technique. In one example,the implantable sensor device is directed into a urinary bladder via theurethra. In one such embodiment, the implantable sensor device includesa stabilizer or other structure that expands following disposition inthe bladder. As a result, the implantable sensor device is retained inthe bladder without blocking flow to the urethra.

Though particular aspects of the system have been described inconjunction with its use in measuring pressure, it is understood thatthe system can also be used with an implantable sensor for sensingmanifestations of other physical parameters such as, by way of example,but not by way of limitation, sensing blood gasses or other gasses(e.g., O₂, CO₂), pH, electrocardiograms, and blood glucose. In anotherexample, the system is used in conjunction with ultrasonic measurements(e.g., measuring blood flow, or measuring heart wall thickness fordetermining contractility, etc.).

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. An apparatus for measuring a blood pressure in aheart chamber in a heart in a living organism, the apparatus comprising:a housing adapted for being disposed in the heart; a pressuretransducer, adapted for being disposed in the heart, the pressuretransducer providing a pressure signal based on the blood pressure inthe heart chamber; a wireless communication circuit, carried by thehousing and coupled to the pressure transducer, the communicationcircuit wirelessly transmitting pressure information out of the heartbased on the pressure signal; at least one stabilizer, coupled to thehousing, and adapted for stabilizing the housing within the heart; and apressure transmission catheter adapted for receiving the pressure in theheart chamber, the pressure transmission catheter being coupled to thepressure transducer via a flowable medium to communicate the pressure inthe heart chamber to the pressure transducer.
 2. The apparatus of claim1, in which the pressure transmission catheter includes a biocompatiblegel-like tip that is adapted to receive the pressure in the heartchamber.
 3. A method of sensing a parameter in a heart chamber in aheart in a living organism, the method comprising: receiving a physicalmanifestation of the parameter in the heart chamber at a sensor devicedisposed within the heart; converting, within the heart, the physicalmanifestation of the parameter into a sensor signal; and generating awireless signal based on the sensor signal, the wireless signalgenerated within the heart.
 4. The method of claim 3, further comprisingtranslumenally disposing the sensor device in the heart.
 5. The methodof claim 3, in which communicating information includesradio-telemetering the information from the heart.
 6. The method ofclaim 3, in which communicating information includes inductivelycoupling the information from the heart.
 7. The method of claim 3, inwhich communicating information includes: receiving energy at a passivetransponder in the heart; powering the passive transponder from theenergy received; and transmitting information from the heart using thepowered passive transponder.
 8. The method of claim 3, furthercomprising: receiving energy; and recharging a battery located in theheart using the energy received.
 9. The method of claim 3, in whichcommunicating information includes: conducting a current through atleast a portion of the living organism; and receiving, at a receiverthat is outside the heart, a signal that is based on the current. 10.The method of claim 3, in which communicating information includes:conducting a current through at least a portion of the living organism;and receiving, at a receiver that is external to the living organism, asignal that is based on the current.
 11. The method of claim 3, furthercomprising receiving the information at a receiver that is carried by animplantable medical device located within the living organism.
 12. Themethod of claim 3, further comprising: receiving the information at areceiver that is external to the living organism; and storing theinformation in a memory in the receiver.
 13. The method of claim 12,further comprising transferring the information from the receiver to acomputer.
 14. The method of claim 13, further comprising analyzing theinformation in the computer.
 15. The method of claim 14, furthercomprising displaying to a user an indicator based on the information.16. The method of claim 3, in which the heart chamber is selected from agroup consisting essentially of a right atrium, a right ventricle, aleft atrium, and a left ventricle.
 17. The method of claim 3, furthercomprising receiving the information at a receiver that is carried by ancardiac rhythm management device located within the living organism. 18.The method of claim 17, further comprising adjusting therapy deliveredto the heart by the cardiac rhythm management device, wherein adjustingtherapy is based on the sensor signal wirelessly communicated from theheart.
 19. A method of measuring blood pressure in a heart chamber in aheart in a living organism, the method comprising: receiving the bloodpressure in the heart at a pressure transducer device; transducing,within the heart, the blood pressure in the heart chamber into apressure signal; and generating a wireless signal based on the pressuresignal, the wireless signal generated within the heart.
 20. The methodof claim 19, further comprising translumenally disposing the pressuretransducer device in the heart via a placement catheter.
 21. The methodof claim 19, in which receiving the blood pressure includescommunicating the blood pressure from the heart to the pressuretransducer via a flowable medium.
 22. The method of claim 21, in whichreceiving the blood pressure includes receiving the blood pressure at adistal end of a pressure transmission catheter and transmitting theblood pressure from the heart to the pressure transducer via a flowablemedium within the pressure transmission catheter.
 23. The method ofclaim 22, in which transducing the pressure includes: receiving theblood pressure at the pressure transducer from the flowable mediumwithin the pressure transmission catheter; varying at least oneresistance in the pressure transducer based on the received pressure;and providing a resulting electrical signal, which includes pressureinformation based on the varying resistance of the pressure transducer.24. The method of claim 19, in which communicating pressure informationincludes radio-telemetering the pressure information from the heart. 25.The method of claim 19, in which communicating pressure informationincludes inductively coupling the pressure information from the heart.26. The method of claim 19, in which communicating pressure informationincludes: receiving energy at a passive transponder; powering thepassive transponder from the received energy; and transmitting pressureinformation from the heart using the powered passive transponder. 27.The method of claim 19, in which communicating pressure informationincludes: conducting a current through at least a portion of the heart;and receiving, at a receiver that is outside the heart, a signal that isbased on the current.
 28. The method of claim 19, which communicatingpressure information includes: conducting a current through at least aportion of the heart; and receiving, at a receiver that is external tothe living organism, a signal that is based on the current.
 29. Themethod of claim 19, further comprising: translumenally disposing apressure transducer device within the heart; and stabilizing thepressure transducer device within the heart.
 30. The method of claim 29,in which stabilizing the pressure transducer device includes securingthe pressure transducer device to the heart.
 31. The method of claim 30,in which securing the pressure transducer to the heart includesimplanting the pressure transducer substantially within a wall of theheart.
 32. The method of claim 19, in which the heart chamber isselected from a group consisting essentially of a right atrium, a rightventricle, a left atrium, and a left ventricle.
 33. The method of claim19, further comprising: receiving the wirelessly communicated bloodpressure information at a cardiac rhythm management device; andadjusting therapy delivered to the heart by the cardiac rhythmmanagement device based on the wirelessly communicated blood pressureinformation.